1. Field of the Invention
The present invention relates to a hiqh-frequency circuit apparatus and a communication apparatus used for, e.g., a microwave band.
2. Description of the Related Art
For instance, a transmitting frequency band of 1850 to 1910 MHz is required for a transmitting side circuit of an antenna duplexer used for a PCS, a receiving frequency band of 1930 to 1990 MHz is required for a receiving side circuit. Both of transmitting side and receiving side circuits need to have a wide passing band of 60 MHz. Separation of 20 MHz is assured to separate the transmitting frequency band and receiving frequency band, and the separation between them is extremely small.
The antenna duplexer synthesizes a phase of the transmitting side circuit with a phase of the receiving side circuit. In case of the PCS, the transmitting side circuit is set to have a high impedance of the receiving frequency band of 1930 to 1990 MHz (become open), and the receiving side circuit is set to have a high impedance of the transmitting frequency band of 1850 to 1910 MHz (become open). Accordingly, the phase of the transmitting side circuit is synthesized with that of the receiving side circuit desirably.
FIG. 8 shows a circuit construction example of an antenna duplexer 1, and FIG. 9 is a perspective view of the antenna duplexer 1 where parts are mounted on a circuit board 40. In case of the PCS system, the antenna duplexer 1 has narrow separation between the transmitting frequency band and the receiving frequency band of 20 MHz, so that the transmitting frequency band is divided into two bands, i.e., a band of 1850 to 1880 MHz and a band of 1880 to 1910 MHz, the receiving frequency band is divided into two bands, i.e., a band of 1930 to 1960 MHz and a band of 1960 to 1990 MHz, and thus the passing band is made narrow and the separation is made wide. That is, a reactance element (PIN diode) capable of controlling a voltage is connected to a resonator, and the reactance element and resonator are voltage-controlled. Consequently, it is possible to switch the two kinds of passing bands which a transmitting side circuit 25 and a receiving side circuit 26 have, respectively, and the number of filter stages is reduced to have a small size and high characteristics.
Referring to FIGS. 8 and 9, Tx denotes a transmitting terminal; Rx a receiving terminal; ANT an antenna terminal; 2 and 3 resonators of the transmitting side circuit 25; 4 to 6 resonators of the receiving side circuit 26; L1 and L11 coupling coils; C1 and C2 coupling capacitors which decide the magnitude of a blocking band attenuation amount; L9 and L10 inductances for resonance; C5, C6, and C24 capacitors; C3, C4, and C7 to C9 capacitors for variable frequency band; D2 to D6 PIN diodes; L2, L3, and L6 to L8 choke coils; R1, R2, C22, and C23 resistors and capacitors for supplying a control voltage; L20, L21, C15 coils and capacitors comprising phase circuits; and C11 to C14 coupling capacitors. Dielectric resonators are used for the resonators 2 to 6.
The antenna duplexer 1 outputs a transmitting signal, which is inputted from a transmitting circuit system to the transmitting terminal Tx, from the antenna terminal ANT via the transmitting side circuit 25, and also outputs a receiving signal inputted from the antenna terminal ANT from the receiving terminal Rx to a receiving circuit system via the receiving side circuit 26.
CONT1 denotes a voltage control terminal for voltage-controlling the PIN diodes D2 and D3 in the transmitting side circuit 25; and CONT2 a voltage control terminal for voltage-controlling the PIN diodes D4 to D6 in the receiving side circuit 26. If applying a positive voltage to the voltage control terminals CONT1 and CONT2, the PIN diodes D2 to D6 are turned on, and the antenna duplexer 1 operates at a LOW channel. In other words, as shown in FIG. 10, the passing band of the transmitting side circuit 25 is set to 1850 to 1880 MHz, and that of the receiving side circuit 26 is set to 1930 to 1960 MHz. On the contrary, if setting the control voltage to 0V to prevent a voltage from being applied to the voltage control terminals CONT1 and CONT2, alternatively, applying a negative voltage to the voltage control terminals CONT1 and CONT2, the PIN diodes D2 to D6 are turned off and the antenna duplexer 1 operates at a HIGH channel. That is, as shown in FIG. 10, the passing band of the transmitting side circuit 25 is set to 1880 to 1910 MHz and that of the receiving side circuit 26 is set to 1960 to 1990 MHz.
A cellular phone is set to a standby mode of a receiving wave for time excluding communication time. If the frequency of the receiving wave standby mode is equal to 1930 MHz and the cellular phone then enters the receiving wave standby mode while applying the positive voltage to the voltage control terminals CONT1 and CONT2 in the antenna duplexer 1, there might be arisen problems such that a battery of the cellular phone is wasted fast and the receiving wave standby time becomes short.
With regard to the countermeasures against the foregoing, it is devised that the control voltage of the voltage control terminal CONT1 is set to 0V and the positive voltage is applied only to the voltage control terminal CONT2. Thereby, a consumption current flows only to the receiving side circuit 26 for receiving wave standby mode and thus it is able to suppress the waste of the battery. However, in a system, e.g., the PCS such that the transmitting frequency band has a frequency lower than that of the receiving frequency band, if turning off the PIN diodes D2 and D3 in the transmitting side circuit 25 and turning on the PIN diodes D4 to D6 in the receiving side circuit 26, as shown in FIG. 11, the separation is made extremely narrow between the passing band (1880 to 1910 MHz) in the transmitting side circuit 25 and the passing band (1930 to 1960 MHz) in the receiving side circuit 26. As a consequence, it is made difficult to set the transmitting side circuit 25 to have a high impedance (become open) at the receiving frequency band of 1930 to 1960 MHz, thereby arising a new problem to increase a loss for inserting the receiving side circuit 26.
FIG. 12 is a graph showing a result to measure a passing characteristic S32 and a reflecting characteristic S22 of the receiving side circuit 26, when applying the positive voltage to the voltage control terminals CONT1 and CONT2 (refer to FIG. 8). In this figure, the loss for inserting the receiving side circuit 26 is equal to 3.3 dB. By contrast, FIG. 13 is a graph showing a result to measure the passing characteristic S32 and the reflecting characteristic S22 of the receiving side circuit 26, when applying the positive voltage only to the voltage control terminal CONT2. Referring to FIG. 13, a waveform distortion is caused at a portion indicated by a circle A. In this figure, the loss for inserting the receiving side circuit 26 deteriorates to 5.0 dB.
To overcome the above described problems, preferred embodiments of the present invention provide a high-frequency circuit apparatus and a communication apparatus having a small consumption current and a low inserting loss.
One preferred embodiment of the present invention provides a high-frequency circuit apparatus comprising:
an antenna duplexer of a frequency variable type having a first external terminal, a second external terminal, and an antenna terminal;
a first change-over switch which is electrically connected to the antenna terminal;
a second change-over switch which is electrically connected to the second external terminal; and
a filter which is electrically connected across the first change-over switch and the second change-over switch. Herein, the first external terminal is, e.g., a transmitting terminal, the second external terminal is, e.g., a receiving terminal, and the filter is, e.g., a filter for reception.
In case of a receiving wave standby mode at a channel frequency band in which it is necessary to flow a consumption current to the antenna duplexer, the antenna duplexer is switched to the filter by first and second change-over switches, and the receiving wave is allowed to pass through the filter, not through the antenna duplexer. Accordingly, it is unnecessary to flow the consumption current to the antenna duplexer, thereby decreasing the amount of consumption current for the receiving wave standby mode.
As for the first and second change over switches, a GaAs switch and a PIN diode switch are used and thus the switch size is miniaturized and also the switching operation becomes fast. As for the filter, a surface acoustic wave filter, a coil, and a capacitor are combined and constructed thereby using the thus-obtained filter. Consequently, the filter is miniaturized.
Further, according to the present invention, there is provided a communication apparatus comprising any one of the high-frequency circuit apparatuses having the aforementioned features, and to thereby suppress the amount of consumption current for receiving wave standby mode and diminish the loss of the receiving side circuit.